On the improved Dividing Engine. 373 



-soon, when I will be glad that the anonymous critic, who 

 says I have never given any proof, would come and exa- 

 mine the engine, and what ii produces. 



I have only one more remark to offer, for the sake of those 

 who may hereafter make dividing engines : it is to correct 

 a mistaken notion, which I find exists among men even in 

 the mathematical line; some of whom imagine, that the 

 way to rack an engine, is to press the cutter to the edge of 

 the wheel, and to go on at once all round, by turning the 

 screw-cutter until they have effected a complete revolution 

 of the wheel ; trusting, at the same time, that they have 

 got the wheel exactly of the size that will take in the 

 number of teeth that they want, by which means they con- 

 ceive there could exist no error. But such a method, I 

 believe, was never attempted, and I believe never will; 

 and could it be done, the wheel would be too little for the 

 screw, when the teeth became full. To such as might be 

 misled bv this idea, the following directions may be useful: 

 The wheel, at first, must be kept as large as possible for 

 the screw-cutter to act properly, and by joining different 

 portions of the teeth, which is done from divisions laid 

 down for the purpose as a guide. Hoping that this com- 

 munication may prove useful, 



I am, sir, 

 Blewitts-buiJdings, Your humble servant, 



»^°^--'^«'^- _ James Allan. 



P. S. Nov. 13. — Since I wrote the above, I have re- 

 ceived the subjoined letter from Mr. Bacon, who has been 

 well known, for a long time, in the mechanical world for 

 hisiuirenuitv. He has had a hand in niaki no; several of the 

 old engines ; and he has al.'o made several straight line en- 

 gines ttiat act with rack and screw ! To his present engine 

 he has added a circular motion, which he has done upon 

 my principle, and which enables him to speak from expe- 

 rience, having produced full and complete teeth. 



Mr. Bennett, of Charles-street, Hatton-garden, mathe- 

 matical instrument maker, whose opinion is also subjoined, 

 is a man of considerable experience in the mathematical 

 line; he was foreman to the late Mr. Ramsden, and con- 

 siders my invention to be a great improvem(^nt : he has 

 favoured me with his opinion, in writing, which I here- 

 with send you. 



To Mr. James Allan. 



Sir— Agreeably to your request, I give you my opinion 

 of your improvement on dividing engines, which is the 

 A a 3 



